Building materials for forming exterior walls and interior walls of buildings include ceramic siding boards, metal siding boards, and ALC (autoclaved lightweight aerated concrete) boards.
Recently, requirements for exterior design of the aforementioned building materials have increased. As one measure for such requirements, mirror finishing, in which surfaces of building materials are finished into smooth glossy faces like a mirror, has been examined.
PTL 1 discloses a building material provided with a mirror-finished coating. The building material includes a first mirror coating and a second mirror coating formed on a surface of a base material.
Building materials are typically stored and transported in a state in which a plurality of building materials are stacked on each other. The surfaces of the building materials are protected with packing sheets and protective sheets to prevent the surfaces of the building materials from being damaged during storage and transport.
Meanwhile, to prevent the surfaces of building materials from being damaged during construction of the building materials into a building, it is desired that the construction be performed in a state in which the surfaces of the building materials are protected.
PTL 2 describes affixing a protective layer (protective sheet), such as a packing sheet, to a surface of a coating of a building material that is a fiber-cement component. PTL 2 describes that an adhesive force between the coating and the protective sheet is set to 15 to 190 g/inch (converted to 0.12 to 1.47 N/20 mm).